A piece of unknown debris floats just under the water in this image taken by a Royal New Zealand P3 Orion while it searches for missing Malaysia Airlines Flight MH370, over the Indian Ocean. Photo: AFP Photo

Royal New Zealand Air Force P-3 Orion's captain, Wing Commander Rob Shearer watches out of the window of his aircraft while searching for the missing Malaysia Airlines Flight MH370 in the southern Indian Ocean. Photo: AP Photo

Objects sighted at sea on Sunday by an Australian Orion searching for missing Malaysia Airlines flight MH370 have been identified as fishing buoys, nets and other ocean junk.

The crew of a P-3 Orion captained by Flight Lieutenant Russell Adams reported at least four orange objects, each more than two metres in size, during an 11-hour mission over the Australian search zone, west of Perth, on Sunday.

"We were able to detect many objects in the water today," Flight Lieutenant Adams said on the tarmac at RAAF Pearce on Sunday.

"We were able to rule a few out as fishing buoys and fishing nets, however, of interest today we did encounter an area within approximately five nautical miles which included at least four orange coloured objects greater than approximately two metres in size each.”

But he stressed that the objects had not been identified and further investigation and analysis were required.

“However, for my crew, from our perspective this ... gave us the most promising leads," he said.

Australian search authorities ruled out the objects as possible plane debris hours later, based on images provided by the crew.

“The objects have been described as fishing equipment and other flotsam,” an Australian Maritime Safety Authority spokeswoman told Fairfax Media.

There have been growing incidents of object sightings at sea following a dramatic shift in the search zone to an area about 1850 kilometres west of Perth on Friday.

The move closer to land had followed a revision of MH370's likely movements by international air crash investigators in Malaysia.

In the days that followed, aircraft, including a Royal New Zealand Air Force P-3 Orion, a Chinese Ilyushin IL-76 and two Australian P-3 Orions, reported more than 10 sightings, at least one of which was later found to be a “distinctive fishing object”, AMSA said in a statement on Saturday.

“The objects cannot be verified or discounted as being from MH370 until they are relocated and recovered by ships,” AMSA said. “It is not known how much flotsam, such as from fishing activities, is ordinarily there.”

Although eight ships have now arrived in the search zone, there has yet to be confirmation any of the items discovered by air crews are linked to the missing flight.

Meanwhile, the ADV Ocean Shield, which is carrying the mission's only black box pinger locator has been delayed departing from a Perth naval base.

The Ocean Shield was due to leave HMAS Stirling about 9pm to undertake equipment trials near Rottnest Island before heading for the search zone, but has been delayed by an hour and half.

There had been no significant object sightings by late afternoon on Monday, an AMSA spokeswoman said. The crew of a New Zealand P-3 Orion spotted 14 objects at sea, photographed two and dropped a GPS buoy on one, but none were considered significant.

"The JACC will be headed by Air Chief Marshal Angus Houston, the former Chief of the Defence Force Australia.

The JACC will co-ordinate operations between all Australian government agencies and international search teams.

As per the information that we have received from the Australian authorities, the area of search today is 254,000 square kilometres.

Today, nine military aircraft and one civilian aircraft travelled to the search area. These planes were:

• two Malaysian C-130.• one Chinese Ilyushin IL-76. • one Japanese Coast Guard G5.• one Australian P3 Orion.• one New Zealand P3 Orion.• one New Zealand civilian aircraft.• one American P8 Poseidon.• one Japanese P3 Orion.• one Korean P3 Orion.

Today eleven ships were also deployed to the search area:

• Eight Chinese ships: - the Xue Long,- the Kunlunshan,- the Haikou,- the Qiandaohu Jian,- the Jing Gang Shan,- the Haixun,- the Dong Hai Jian,- and the Nan Hai Jian.• Three Australian ships: - the HMAS Success,- the HMAS Toowoomba- and MV Barkley Pearl, which is currently transiting in the search area.

The Malaysian ship, the KD Lekiu, is expected to arrive in the search area on 3 April.

The ADV Ocean Shield - fitted with the towed pinger locator and a Bluefin 21 autonomous underwater vehicle - is due to arrive in the search area on 3 April."